Abstract:

Provided are a method of recovering valuable metals from IZO scrap,
wherein indium and zinc are recovered as hydroxides by using an IZO scrap
as both an anode and a cathode, and performing electrolysis while
periodically reversing polarity; and a method of recovering valuable
metals from IZO scrap, wherein the hydroxides of indium and zinc obtained
by the electrolysis are roasted and indium and zinc are recovered as
oxides. Specifically, provided is a method which enables the efficient
recovery of indium and zinc from IZO scrap such as a spent indium-zinc
oxide (IZO) sputtering target and IZO mill ends arising during the
manufacture of such a sputtering target.

Claims:

1. A method of recovering valuable metals from IZO scrap, wherein indium
and zinc are recovered as hydroxides by using an IZO scrap as both an
anode and a cathode, and performing electrolysis while periodically
reversing polarity.

2. The method of recovering valuable metals from IZO scrap according to
claim 1, wherein the hydroxides of indium and zinc obtained by the
electrolysis are roasted and indium and zinc are recovered as oxides.

3. The method of recovering valuable metals from IZO scrap according to
claim 2, wherein the hydroxides of indium and zinc obtained by the
electrolysis are subject to acid leaching to obtain a solution of indium
and zinc, zinc is eliminated from the solution, and indium is further
recovered by electrolysis.

4. The method of recovering valuable metals from IZO scrap according to
claim 1, wherein the hydroxides of indium and zinc obtained by the
electrolysis are subject to acid leaching to obtain a solution of indium
and zinc, zinc is eliminated from the solution, and indium is further
recovered by electrolysis.

Description:

TECHNICAL FIELD

[0001]The present invention relates to a method of recovering valuable
metals from IZO scrap such as a spent indium-zinc oxide (IZO) sputtering
target or IZO mill ends arising during the manufacture of such a target
(hereinafter collectively referred to as the "IZO scrap" in this
specification). Incidentally, "recovery of valuable metals" as used
herein shall include the recovery of compounds of oxides, hydroxides and
the like, which have valuable metal as their component.

BACKGROUND ART

[0002]In recent years, an indium-zinc oxide (In2O3--ZnO:
generally known as IZO) sputtering target is being widely used for a
transparent conductive thin film of an LCD device and the like. In many
cases, however, a thin film is formed on a substrate or the like by
employing the sputtering method as the thin-film forming means.

[0003]Although the sputtering method as the thin-film forming means is a
superior method; for example, if a sputtering target is used to form a
transparent conductive thin film, the target will not be consumed
uniformly. A portion of the target with severe consumption is generally
referred to as an eroded portion, and the sputtering operation is
continued until immediately before a backing plate supporting the target
becomes exposed due to the further consumption of the eroded portion.
This target is subsequently replaced with a new target.

[0004]Accordingly, a spent sputtering target will have numerous non-eroded
portions; that is, unused portions of the target, and all of these
portions become scrap. Moreover, even during the manufacture of an IZO
sputtering target, scraps (mill ends) will arise from grinding dust and
cutting wastage. Generally speaking, the scrap contains zinc oxide (ZnO)
at approximately 10.7 wt %, but the scrap is mostly indium oxide
(In2O3).

[0005]Because high-purity materials are used as the IZO sputtering target
material and because indium is particularly expensive; in general, indium
and zinc are simultaneously recovered from the foregoing scrap materials.
As this kind of indium recovery method, conventionally, a method that
combines wet refining such as the acid solution process, ion exchange
method and solvent extraction method has been used.

[0006]For instance, there is a method of subjecting an IZO scrap to
cleansing and pulverizing, dissolving the obtained material with
hydrochloric acid, precipitating and eliminating impurities, such as
zinc, lead and copper, as sulfide by passing hydrogen sulfide through the
solution, thereafter adding ammonia to neutralize the solution, and
recovering the resulting indium hydroxide.

[0007]Nevertheless, the indium hydroxide obtained by the foregoing method
has inferior filtration property, requires long operational process, and
contains large amounts of impurities such as Si and Al. In addition, with
the created indium hydroxide, since the grain size and grain size
distribution will vary depending on the neutralization condition,
maturization condition and other conditions, there is a problem in that
the characteristics of the IZO target cannot be stably maintained upon
subsequently manufacturing such IZO target.

[0008]Conventional technology (similar technology) and its advantages and
disadvantages are described below.

[0009]As one example of such conventional technology, there is an etching
method of a transparent conductive film including the steps of reducing
an ITO film deposited on a substrate by an electrochemical reaction in
the electrolyte, and dissolving the reduced transparent conductive film
in the electrolyte (refer to Patent Document 1). However, the object of
this method is to obtain a mask pattern with high precision, and relates
to technology that is different from the recovery method.

[0010]For pretreatment for recovering valuable metals from ITO, there is
also technology of isolating, in the electrolyte, the impurities
contained in an In-based brazing filler material used in the bonding with
the backing plate (refer to Patent Document 2). Nevertheless, this method
does not relate to direct technology of recovering valuable metals from
ITO.

[0011]Moreover, upon recovering indium from an intermediate obtained as a
by-product of the zinc refining process or from an ITO scrap, disclosed
is technology of separating tin as halogenated stannate, performing
reduction treatment with hydrochloric acid or nitric acid solution,
subsequently adjusting the pH of this aqueous solution to be between 2
and 5, reducing metallic ions of iron, zinc, copper, thallium and the
like in order to make the metallic ions into a substance that will not
precipitate easily, and isolating the indium component in the aqueous
solution (refer to Patent Document 3). With this technology, however,
there are problems in that the refining process is complicated and a
superior refining effect cannot be expected.

[0012]Further, as a method of recovering high-purity indium, disclosed is
technology of dissolving ITO with hydrochloric acid, adding alkali
thereto to make the pH within a range of 0.5 to 4, eliminating tin as
hydroxide, subsequently blowing hydrogen sulfide gas in order to
eliminate hazardous materials such as copper and lead as sulfide, and
electrowinning indium metal by performing electrolysis using the obtained
solution (refer to Patent Document 4). There is a problem with this
technology in that the refining process is complicated.

[0013]In addition, proposed is a method of dissolving an ITO
indium-containing scrap with hydrochloric acid to obtain an indium
chloride solution, adding a sodium hydroxide solution to this solution to
eliminate tin as tin hydroxide, additionally adding a sodium hydroxide
solution thereto after the elimination to obtain indium hydroxide,
filtering the obtained indium hydroxide to obtain indium sulfate from the
filtered indium hydroxide, and obtaining indium by electrowinning with
the indium sulfate (refer to Patent Document 5). Although this is an
effective method with a significant refining effect, there is a drawback
in that the process is complicated.

[0014]Also proposed is a method of recovering indium including the steps
of dissolving an ITO indium-containing scrap with hydrochloric acid to
obtain an indium chloride solution, adding a sodium hydroxide solution to
the indium chloride solution to eliminate tin contained in the scrap as
tin hydroxide, substituting indium with zinc from the solution after
eliminating the tin hydroxide, and thereafter recovering indium (refer to
Patent Document 6). Although this is also an effective method with a
significant refining effect, there is a drawback in that the process is
complicated.

[0015]Additionally disclosed is a method of recovering metallic indium
including the steps of extracting suboxide-containing cast scrap floating
on molten metallic indium, introducing this into an atmosphere furnace,
introducing argon gas into the furnace after vacuating the furnace once,
heating the furnace to a prescribed temperature, and reducing the
suboxide-containing cast scrap (refer to Patent Document 7).

[0016]Although this is in itself an effective method, there is a drawback
in that this is not a fundamental recovery method from IZO scrap. In
light of the above, a method that is efficient and with a versatile
recovery process is being sought.

[0024]In order to overcome the foregoing problems, the present invention
provides a method of efficiently recovering indium and zinc from IZO
scrap such as a spent indium-zinc oxide (IZO) sputtering target or IZO
mill ends arising during the manufacture of such a target.

[0025]The present invention provides a method of recovering valuable
metals from IZO scrap by performing electrolysis to such IZO scrap in a
pH-adjusted electrolyte to obtain indium and zinc as hydroxides of indium
and zinc.

[0026]The method of recovering valuable metals from IZO scrap according to
the present invention is unique in that the IZO scrap is used as both an
anode and a cathode. In the foregoing case, electrolysis is performed
while periodically reversing polarity of both the anode and cathode; that
is, electrolysis is performed while periodically alternating the polarity
(interconversion of anode polarity cathode polarity).

[0027]Consequently, it is possible to efficiently recover valuable metals
as the hydroxides of indium and zinc. This kind of technology did not
exist conventionally. Nor is there any document that suggests this kind
of method. Thus, the method of recovering valuable metals from IZO scrap
according to the present invention is a basic invention.

[0028]Since an IZO scrap is an oxide-system ceramic, it would not normally
be possible to envisage recovering valuable metals by the electrolytic
method. Nevertheless, IZO itself possesses conductive property even
though it is an oxide-system ceramic. In light of this point, the present
invention attempted to recover valuable metals (for instance, indium or
zinc and the compound thereof) by electrolysis, and succeeded.

[0029]It is well known that IZO itself possesses conductive property. This
is considered to be due to the oxygen defect in the IZO oxide as a
sintered compact of zinc oxide (ZnO) and indium oxide (In2O3).
The present invention utilizes the conductive property of the IZO itself.
Nevertheless, it should be understood that the knowledge and judgment
that the conductive property inherent in IZO itself enables a recovery of
valuable metals by electrolysis could only be realized through the
implementation of numerous experiments.

[0030]When performing a conventional method of recycling IZO scrap; a
recycled IZO is manufactured by pulverizing the IZO scrap, dissolving it
with strong acid, and then going through a process in that a plurality of
process steps, such as reduction, substitution, sulfurization,
precipitation, neutralization, filtration, solvent extraction, ion
exchange and casting, are arbitrarily combined.

[0031]The problems in the foregoing process steps are that impurities are
incorporated during the pulverization process of IZO scrap, and the
overall process becomes more complicated since it is necessary to
eliminate the impurities incorporated during the pulverization process at
the subsequent process steps.

[0032]Thus, it should be easy to understand that it has an extremely
significant benefit that valuable metals can be recovered directly from
IZO scrap by electrolysis.

[0033]With the method of recovering valuable metals from IZO scrap
according to the present invention, it is desirable to further reverse
the polarity of the anode and cathode when the voltage rises beyond a
certain level during the electrolysis. As described later, the polarity
conversion of the anode and the cathode is a means for improving the
recovery efficiency, and the voltage becomes an index thereof.
Accordingly, it is possible to detect the point of time when the voltage
rises, and set the timing to reverse the polarity accordingly.

[0034]Generally speaking, if the equipment is fixed, it is possible to
constantly grasp the optimal condition of the reverse timing. Thus, it is
also possible to reverse the polarity in certain intervals according to
the foregoing optimal condition. Accordingly, it should be understood
that the timing to reverse the anode and cathode polarity can be
arbitrarily controlled and is not constrained by the foregoing
conditions.

[0035]Moreover, during the foregoing electrolysis, it is preferable to
reverse the polarity of the anode and the cathode in 1-minute to
10-minute periods. However, it is a condition that the timing to reverse
the polarity can also be arbitrarily changed according to the capacity of
the electrolytic bath, amount of IZO scrap, current density, voltage,
current, and type of electrolyte. It should be easy to understand that
the foregoing condition merely shows a preferable condition, and the
present invention is not constrained by such condition described above.

[0036]Upon recovering valuable metals from IZO scrap according to the
present invention, a neutral electrolyte is used to perform the
electrolysis and valuable metals are recovered as the hydroxides of
indium and zinc. It is desirable to adjust the initial pH of the
electrolyte to be between 2 and 12. This is a preferable condition for
efficiently recovering the hydroxides of indium and zinc.

[0037]As the electrolyte, it is desirable to select a fluid that does not
generate hazardous gas and is a material of which component will not be
incorporated as an impurity when recovering the hydroxides of indium and
zinc. Thus, a solution of sodium sulfate, sodium chloride, sodium
nitrate, ammonium sulfate, ammonium chloride, ammonium nitrate, potassium
chloride, potassium nitrate, potassium sulfate and the like may be
arbitrarily selected and used.

[0038]Nevertheless, so as long as the solution can be used to perform
electrolysis of the IZO scrap while giving consideration to the
production efficiency, it should be understood that solutions other than
those listed above may also be used as the electrolyte. The selection of
the electrolyte is merely to arbitrarily select a solution that
accommodates the condition of being able to electrolyze the IZO scrap,
and it is obvious that such selection is not the essence of the present
invention.

[0039]Although the present invention achieves its object by recovering the
hydroxides of indium and zinc that were obtained by electrolysis upon
recovering valuable metals from IZO scrap, it is also possible to recover
indium and zinc as oxides by roasting the hydroxides of indium and zinc.

[0040]As described above, if it is possible to once obtain the hydroxides
of indium and zinc from the IZO scrap, these can be roasted in order to
obtain a mixture of indium oxide and zinc oxide, and the obtained
material can be used as is as the IZO raw material. Moreover, as needed,
indium oxide or zinc oxide may be added to change the ingredient amount
or other elements may be added, and the IZO target can be easily recycled
by sintering the resultant. The present invention covers all of the
foregoing aspects.

[0041]In addition, the hydroxides of indium and zinc that were obtained by
way of electrolysis as described above may be subject to acid leaching to
obtain a solution of indium and zinc, this solution can be pH-adjusted to
eliminate zinc as zinc hydroxide, and indium can thereby be recovered by
way of electrowinning.

[0042]As described above, the method of recovering valuable metals from
IZO scrap according to the present invention enables to recover
high-purity indium and zinc as hydroxides, which retain the purity of IZO
scrap itself if such IZO scrap subjected to electrolysis is a scrap
formed from high-purity material. It goes without saying that this is a
significant advantage of the present invention. The present invention
yields superior effects of no longer requiring such complicated processes
and process of eliminating impurities incorporated during manufacture as
were required in the past, and being able to increase the production
efficiency and recover high-purity valuable metals.

[0043]The electrolytic condition such as the current density is not
uniformly decided since the subject is scrap such as mill ends, and
electrolysis is performed by arbitrarily selecting the current density
according to the amount of mill ends and the nature of material. The
liquid temperature of the electrolyte solution is generally set to a
range of 0 to 100° C., but room temperature (15 to 30° C.)
will suffice.

[0044]Since electrolysis is simply performed by using IZO scrap of an
indium-zinc oxide (IZO) sputtering target or IZO mill ends arising during
the manufacture of such a target as the anode and cathode, the present
invention is a superior method which enables simple and efficient
recovery of valuable metals as hydroxides of indium and zinc, and as a
mixture of indium oxide and zinc oxide. Moreover, the method of
recovering valuable metals from IZO scrap according to the present
invention enables to recover high-purity indium and zinc as hydroxides,
which retain the purity of IZO scrap itself if such IZO scrap subjected
to electrolysis is a scrap formed from high-purity material. This is a
significant advantage of the present invention. The present invention
yields superior effects of no longer requiring such complicated processes
and process of eliminating impurities incorporated during manufacture as
were required in the past, and being able to increase the production
efficiency and recover high-purity valuable metals.

BEST MODE FOR CARRYING OUT THE INVENTION

[0045]The present invention is able to easily recover indium and zinc as
hydroxides from indium-containing scrap of the IZO target by
electrolysis. Moreover, by roasting the obtained hydroxides of indium and
zinc, it is possible to efficiently recover valuable metals as a mixture
of indium oxide and zinc oxide.

[0046]The roasting temperature is set to 100 to 1000° C.,
preferably 100 to 500° C. Moisture will remain if the roasting
temperature is less than 100° C., and sintering will occur if the
roasting temperature is higher than 1000° C. Thus, the roasting
temperature is set to be within the foregoing range.

[0048]Since chlorine gas will be generated with a passivation of the anode
if the anion is of chlorine series, and since nitric oxide gas will be
generated and there will be a nitrogen load of the discharged water with
a passivation of the anode if the anion is of nitric acid series;
attention is required to the processing.

[0049]Since sulfuric acid series hardly entail the foregoing problems, it
could be said that a solution of sulfuric acid series would be a suitable
material. Nevertheless, there is no reason that other electrolytes cannot
be used so as long as the foregoing problems can be overcome.

[0050]In addition, it is also possible to use a publicly-known additive
agent in order to improve the current efficiency. As described above, it
should be easy to understand that recycled IZO can be manufactured easily
if indium oxide and zinc oxide can be simultaneously recovered.

[0051]A special electrolytic apparatus is not required. For instance, it
would suffice to perform electrolysis using an IZO scrap subjected to
electrolysis as the anode and the cathode. It is thereby possible to
avoid the increase or inclusion of impurities more than initially
contained in the IZO scrap.

[0052]It is desirable to adjust the electrolytic condition as needed
according to the type of raw material. The only factor to be adjusted in
this case is the production efficiency. Generally speaking, better
productivity can be attained through electrolysis with a large current
and high voltage. Nevertheless, there is no need to limit the conditions
to the foregoing conditions, and such conditions may be arbitrarily
selected.

[0053]Further, although there is no particular limit on the electrolysis
temperature, it is desirable to adjust the temperature to 0 to
100° C. to perform electrolysis. Electrolysis can be sufficiently
performed at room temperature. Scraps such as mill ends may be
respectively placed in an anode box (basket) or a cathode box (basket)
for the electrolysis. If a scrap itself is of a certain size (enough size
that can be used as an electrode), it can be used as an electrode plate
as is.

[0054]When electrical current is applied to the anode formed from IZO
scrap and the cathode formed from IZO scrap and electrolysis is started,
oxygen gas is generated at the IZO scrap anode, and In and Zn as the
component elements of IZO start to dissolve
(IZO→In3++Zn2+).

[0055]The dissolved In and Zn are precipitated in the electrolyte as the
hydroxides of indium and zinc. Although the amount of this dissolution at
the initial stages of the electrolysis is roughly 10 to 50% as the
current efficiency, sludge will appear on the surface of the IZO scrap,
the amount of dissolution will decrease, and the scrap will ultimately
stop dissolving.

[0056]Although the reason for this is not necessarily clear, it is assumed
that the conductivity of the IZO is lost due to the oxygen defect caused
by the oxygen gas that is generated at the anode, whereby the IZO scrap
itself stops energizing and is unable to function as an anode electrode.
In any case, the dissolution of the IZO scrap will not progress under the
foregoing state, and electrolysis becomes difficult. However, if the
generated sludge can be effectively eliminated from the IZO scrap,
dissolution is possible.

[0057]Meanwhile, at the IZO scrap cathode, hydrogen gas is generated
simultaneously with the start of energization, and the IZO scrap is
subject to hydrogen reduction and becomes indium-zinc metal
(IZO+H2→In--Zn metal). The generation of hydrogen is caused
by the electrolysis of water (H2O→1/2H2+OH.sup.-). This
indium-zinc metal is formed on the cathode surface of the IZO scrap.

[0058]However, if the energization time becomes long, the progress stops
in a state where In--Zn metal having a certain thickness is accumulated
on the cathode surface of the IZO scrap, only sponge-like In--Zn oxide
will be formed below the In--Zn metal surface layer, and reduction will
no longer advance.

[0059]It is believed the main causes of interference with the progress of
electrolysis are that the In--Zn metal surface layer is inhibiting the
infiltration of hydrogen, and that current only flows to the In--Zn metal
surface layer and the flow of current to the inside of the IZO scrap with
high resistance is inhibited.

[0060]In this kind of state, the intended electrolysis will be inhibited
at both the IZO scrap anode and cathode. Thus, the polarity of the IZO
scrap anode and cathode is reversed. This is an extremely important
process.

[0061]Consequently, the In--Zn metal that was accumulated on the surface
of the new anode (former cathode) will dissolve. Since the electrolyte is
retained in a neutral area, it will precipitate as hydroxide. The
precipitate obtained thereby can be recovered as the hydroxides of indium
and zinc. The primary reaction formula can be represented as
(In--Zn→In3++Zn2+→In(OH)3+Zn(OH)2).
Although slight generation of oxygen can be acknowledged with the new
anode, the amount is small. With the new anode, In and Zn also dissolve
from the suboxide. These are also considered to precipitate as the
hydroxides of indium and zinc.

[0062]Meanwhile, with the new cathode (former anode), the sludge in a
passive state is reduced with hydrogen that is generated on the cathode
surface, and becomes In and Zn metal.

[0063]Nevertheless, if this state continues, the new anode is also
passivated, and with the new cathode, only the surface layer becomes
In--Zn metal and electrolysis will no longer progress. The polarity is
once again reversed before reaching this state. As a result of repeating
the foregoing process, it is possible to steadily promote the
precipitation of the hydroxides of indium and zinc.

[0064]As a result of adopting this process of periodically reversing the
electrodes, the generation of gas such as hydrogen and oxygen at the
electrode will decrease considerably in comparison to a case that each of
the electrodes is fixed at either the anode or cathode. This demonstrates
that the generated gas is being effectively consumed for oxidization and
reduction.

[0065]The polarity conversion of the anode and the cathode is a means for
improving the recovery efficiency, and the voltage becomes an index
thereof. Accordingly, it is possible to detect the point of time when the
voltage rises, and thereby set the timing to reverse the polarity. If the
equipment is fixed, it is possible to constantly grasp the optimal
condition of the reverse timing. Thus, it is also possible to reverse the
polarity in fixed intervals according to the foregoing optimal condition.

[0066]Moreover, according to the experiments, it is preferable to reverse
the polarity of the anode and the cathode in 1-minute to 10-minute
periods. However, the timing to reverse the polarity is also a condition
that can be arbitrarily changed according to the capacity of the
electrolytic bath, amount of IZO scrap, current density, voltage,
current, and type of electrolyte.

EXAMPLES

[0067]The present invention is now explained in detail with reference to
the

[0068]Examples. These Examples are merely illustrative, and the present
invention shall in no way be limited thereby. In other words, various
modifications and other embodiments based on the technical spirit claimed
in the claims shall be included in the present invention as a matter of
course.

[0070]Electrolysis was performed by using this raw material as the anode
and the cathode and 1 L of electrolyte containing 100 g/L of sodium
sulfate under the following conditions; namely, pH of 9.0 and
electrolysis temperature of 25° C. The voltage was a constant
voltage at 10V, and energization (polarity conversion every 5
minutes×12 cycles) was performed for a total of 600 minutes (10
hours). The current was changed from 2.95 A (at the onset) to 1.2 A (at
the end) during 5 minutes. Consequently, a mixture of indium hydroxide
and zinc hydroxide precipitated in the electrolytic bath.

Example 2

[0071]The mixture of indium hydroxide and zinc hydroxide obtained as
described above was additionally roasted at 150° C., and a mixture
of In oxide (In2O3) and Zn oxide (ZnO) was thereby obtained.
This mixture was approximately 25 g. The resultant ratio obtained by this
method is normally In2O3: 90 wt % and ZnO: 10 wt %, and it
could be used as the raw material of recycled IZO.

Example 3

[0072]The mixture of indium hydroxide and zinc hydroxide obtained by
electrolysis based on the method of Example 1 was additionally subject to
acid leaching with sulfuric acid to obtain a solution of indium and zinc,
and indium was further recovered by electrowinning under the following
conditions; namely, electrolysis temperature of 30° C. and current
density of 2 A/dm2.

[0073]Indium could be recovered by electrolysis after dissolving the
hydroxide with sulfuric acid. The In yield rate was 98%.

Example 4

[0074]Electrolysis was performed by using IZO mill ends equivalent to
Example 1 as the anode and cathode and a solution of 100 g/L of sodium
nitrate as the electrolyte, setting the pH at 10, and with the other
conditions being the same as the conditions of Example 1. Consequently,
indium-zinc hydroxide was obtained. The purity and the recovered amount
in this case were comparable to Example 1.

Example 5

[0075]In the conditions of Example 1, the current was fixed at 2 A, and
the setting was made so that the polarity is reversed when the voltage
becomes 10V or higher (the other conditions are the same as Example 1).
Moreover, the integrated current was also the same as Example 1.
Consequently, the hydroxides of indium and zinc were obtained. The purity
and the recovered amount in this case were comparable to Example 1.

Example 6

[0076]In the conditions of Example 1, only the cycle was changed to
1-minute and 10-minute intervals, and electrolysis was performed with the
other conditions being the same as the conditions of Example 1.
Consequently, approximately 20 g of indium hydroxide (In grade: 69 wt %)
and approximately 2 g of zinc hydroxide (Zn grade: 7.7 wt %) were
obtained. The purity of this mixture of indium hydroxide and zinc
hydroxide was equivalent to the purity of the scrap.

Example 7

[0077]100 kg of IZO scrap was respectively placed in an anode box and a
cathode box, and electrolysis was performed at 10000 AHr of integrated
current under the following conditions; namely, 70 g/L of sodium sulfate
was used as the electrolyte, the pH was set at 10.5, and the reverse
cycle was set to 5-minute intervals. The other conditions were the same
as Example 1. Consequently, approximately 13 kg of hydroxides of indium
and zinc were obtained. The purity of this mixture of indium hydroxide
and zinc hydroxide was equivalent to the purity of the scrap.

Example 8

[0078]Acid leaching was performed with sulfuric acid under the conditions
of Example 3, and the same results were obtained upon performing acid
leaching with nitric acid. As a result of performing electrowinning to
the indium and zinc that was subject to acid leaching with nitric acid, 3
g of indium metal was obtained.

Comparative Example 1

[0079]IZO scrap that is equivalent to Example 1 was only used as the
anode, and a titanium plate was used as the cathode. 70 g/L of sodium
sulfate was used as the electrolyte, the pH was set at 4.5, and
electrolysis was performed for 60 minutes. The total amount of the
obtained oxide of indium and zinc was 0.4 g, and the recovered amount was
considerably less in comparison to Example 1.

Comparative Example 2

[0080]IZO scrap (mill ends) equivalent to Example 1 was used as the raw
material only for the cathode, and insoluble carbon was used as the
anode. Electrolysis was performed by using sodium sulfate as the
electrolyte as in Example 1, and with the other conditions being the same
as the conditions of Example 1. Consequently, only approximately 0.5 g of
indium-zinc metal could be obtained on the surface of the IZO scrap (mill
ends). The yield was considerably inferior in comparison to the Examples.

[0081]Although, in each of the foregoing Examples, IZO (indium oxide-zinc
oxide) mill ends or scraps of which components were approximately 10 wt %
of zinc oxide (ZnO) and the remaining indium oxide (In2O3) were
used, it goes without saying that the electrolytic conditions such as
current density and pH can be arbitrarily changed according to the
component amount of In2O3 and ZnO and the raw material is not
to be considered particularly limited to the foregoing component amount.
In particular, with IZO, the content of zinc oxide (ZnO) varies from 5 wt
% to 30 wt %, and the present invention can also be sufficiently applied
in the foregoing cases.

[0082]In addition, although there are cases where small amounts of
accessory components are added to the IZO, so as long as IZO is the basic
constituent, it goes without saying that the present invention can also
be applied to this case.

[0083]With the present invention, by using an IZO scrap as both an anode
and a cathode and changing the polarity, it is possible to efficiently
recover valuable metals from IZO scrap as a mixture of indium hydroxide
and zinc hydroxide or meta-zincate.

INDUSTRIAL APPLICABILITY

[0084]Since electrolysis is simply performed by using IZO scrap of an
indium-zinc oxide (IZO) sputtering target or IZO mill ends arising during
the manufacture of such a target as the anode and cathode, the present
invention enables simple and efficient recovery of valuable metals as a
mixture of indium hydroxide and zinc hydroxide, and a mixture of indium
oxide and zinc oxide.

[0085]Moreover, with the method of recovering valuable metals from IZO
scrap according to the present invention, so as long as the IZO scrap
itself to be used in the electrolysis is a scrap formed from high-purity
material, it is possible that the obtained material retains the purity of
the scrap without change, and recover a mixture of high-purity indium
hydroxide and zinc hydroxide or a mixture of high-purity indium oxide and
zinc oxide. This is a significant advantage of the present invention. The
present invention yields superior effects of no longer requiring such
complicated processes and process of eliminating impurities incorporated
during manufacture as were required in the past, and being able to
increase the production efficiency and recover high-purity valuable
metals. Thus, the present invention is extremely useful as a method of
recovering valuable metals from IZO scrap.